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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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GLACIERS OF PASSAGE CANAL AND BLACKSTONE BAY        355
Barren Zone. On each side of the terminus of Tebenkof Glacier was a barren zone (bb, Fig. 52), also noted in 1909 by Grant and Higgins. It is 200 to 400 feet in width, but wedges out at a distance of legs than a mile to the southward. The upper edge of this barren zone marks the greatest expansion of Tebenkof Glacier in recent years, for above it is thick mature forest, with trees 16 to 24 inches in diameter and with a few dead trees, still standing at the edge of the forest. The western margin had many dead tree heaps at the edge of the barren zone.
Between the barren zone and the ice the rock surface is prevailingly bare, and upon it are scattered fragments of dead tree trunks, while, where there is soil, flowers, grasses, and scattered young willows, alders and spruces are growing. The upper part of the western barren zone has quite a number of scattered shrubs, but its lower part has almost none. The largest of the alders observed had seven annual rings. This and the 12 year old alders on the terminal moraine indicate that the last expansion of the glacier up to the edge of the barren zone and out to the terminal moraine was at least 12 years before 1910.
Glaciers at the Head of Blackstone BayŚRelationships of Glaciers. This is a group of moderate-sized ice tongues, descending from nev6 fields which surround the head of Blackstone Bay. All of them are cascading glaciers of varying steepness, and only two are tidal, though three others on the eastern side reach almost to tidewater. The name Blackstone Glacier has heretofore been used for the whole group, as if they were distributaries of a single ice cap, but, as they are not lobes of a single glacier, but separate valley glaciers, as few of their n6v6 fields coalesce on the ridges between, it seems desirable to give separate names to each of the ice tongues. The additional names are taken from colleges in Wisconsin. The apparent coalescing of the glaciers, indicated in Fig. 53, would practically disappear if more detailed maps were made which separated the ice tongues from the nev6 on the adjacent mountain slopes. Bipon Glacier, for example, heads in a cirque which has n6ve all over its head and side walls.
At a period of greater expansion all of these glaciers were tributaries to a great ice tongue in Blackstone Bay similar in dimensions to the Tebenkof Glacier. It seems probable that the retreat of this glacier and its separation into distinct ice tongues, while the non-tidal Tebenkof Glacier still extends over 6 miles farther northward, is, in part at least, a result of more rapid melting of the Blackstone ice tongue on account of its ending in salt water.
Blackstone Glacier. Blackstone Glacier heads in unexplored snowfields southwest of the bay, having a moderately-sloping upper portion, fed by numerous small tributaries, and a steeply-cascading terminus, which descends several hundred feet in the last quarter of a mile, terminating in the southwest corner of the bay in a vertical ice cliff over a hundred feet high, from which small bergs are discharged. The glacier is a clean white, severely-crevassed mass reaching tidewater only in the eastern portion, but descending nearly to tidewater for some distance to the west.
On the early maps by Applegate, Mendenhall, and others this glacier is indicated as coalescing with the adjacent Beloit and Northland ice tongues and as extending over half a mile farther north to the southern end of Willard Island. This is probably an error, for Applegate did not go near enough to the glacier to be sure of its relationships, and in 1910 spruce trees, 10 to 12 inches in diameter, were found at sea level on the